Research On The Different Effects Of Metolachlor And Its S-enantiomer On Plant Cytochrome P450 And Soil Enzymes

Racemic product of metolachlor contains two R-enantiomers and two S-enantiomers. S-metolachlor is now widely used instead of rac-metaolachlor for the former is more effective than the latter in herbicidal activity. We have extracted microsomes cytochrome P450 from corn and rice etiolated seedlings and investigated the influence of rac-metolachlor and S-metolachlor on P450 spectrum. It indicated that corn and rice microsomes enzymes have characteristic absorption peak at wavelength 450nm. The content of cytochrome P450, b5 increased greatly with different chemicals treatment. There was also a trend for a slight shift in the absorbance maximum of microsomes from seed treated with different chemical treatment. The shift in the maximum around 450nm by different seed/ seedlings treatment may indicated that different P450 isoforms was being induced by the treatment.The binding of metolachlor and its S-enantiomer to P450 in aqueous solution was studied using UV difference spectrum. The results showed that the UV difference absorption changed rapidly when herbicide concentration increased from 0.8 to 20mg/L. Both corn and rice UV difference spectra were red-shifted when treated with rac-metolachlor and S-metolachlor and the absorption intensity decreased by raising the concentration of rac-metolachlor and S-metolachlor. At the same herbicide concentration, S-metolachlor absorption decreased more greatly than rac-metolachlor, which indicated S-metolachlor was easier to bind with P450 enzymes.Influence of compound pollution of rac-metolachlor or S-metolachlor with Cd on soil catalase and dehydrogenase activity was studied in laboratory. Results indicated that stress of rac-metolachlor or S-metolachlor was imposed, catalase activity was first enhanced and then inhibited; while dehydrogenase activity followed a similar trend, but eventually rose up again. Rac-metolachlor and S-metolachlor showed different enantioselectivity toward catalase activity, while no significant difference was found in enantioselectivity toward dehydrogenase activity. Under the combined pollution of rac-metolachlor or S-metolachlor with Cd, catalase and dehydrogenase activities showed the same trend as under the single metolachlor pollution. With the same level of metolachlor, catalase and dehydrogenase activities were greatly influenced by increase in concentration of Cd; showing that compound pollution of metolachlor and Cd had certain interaction effect on catalase and dehydrogenase activities.